1. Field
The present disclosure is directed to a method and apparatus for mitigating downlink control channel interference. More particularly, the present disclosure is directed to mitigating the problem of downlink interference from a high power base station when a lower power base station is deployed within the coverage area of the high power base station.
2. Introduction
Presently, in telecommunications, a heterogeneous cell, such as a Closed Subscriber Group (CSG) cell, a hybrid cell, a femtocell, a picocell, a relay node, or other heterogeneous cell can use a small coverage cellular base station that can, for example, be used in residential or small business environments. It connects to a service provider network via a wired or wireless backhaul connection. Some heterogeneous cells allow service providers to extend service coverage indoors, especially where access would otherwise be limited or unavailable. A heterogeneous cell can also provide services to the user that may not be available on a conventional macro cell, such as, for example, mobile television services or less expensive calling plan services. The heterogeneous cell incorporates the functionality of a typical base station but extends it to allow a simpler, self-contained deployment.
For example, heterogeneous cells, such as CSG cells or hybrid cells, are cells used for deployment in a campus or are individual cells used for deployment in users' homes. The heterogeneous cells co-exist with macro cells and have a smaller coverage area than macro cells. Unlike macro cells, the heterogeneous cells are unplanned, in that the operator has much less control over their placement and configuration than with macro cells.
Unfortunately, a heterogeneous cell can experience downlink interference from a high power base station (eNB) for a macro-cell when a lower power home cell base station is deployed within the coverage area of the high power eNB.
For example, co-channel and shared channel home-eNB (HeNB) deployments, where at least a part of the deployed bandwidth, is shared with macro-cells are considered to be high-risk scenarios from interference point-of-view. When a terminal, such as wireless user equipment, associated with, such as, connected to or camped on, a HeNB and the HeNB is deployed close to a macro-eNB (MeNB), the MeNB transmissions can severely interfere with the terminal transmissions to the HeNB. Also, in-band decode and forward relaying involves relay nodes (RN) deployed on the same carrier as the overlay macro-cell. In order to enable backwards compatibility, all the common control channels need to be transmitted on RN downlink.
Typically, a MeNB transmits at much higher power, such as 46 dBm for 10 MHz, relative to a heterogeneous-eNB (Het-eNB or HeNB), such as 30 dBm for RN and 20 dBm for a HeNB for 10 MHz. Therefore, the coverage of MeNB is typically larger and there exists a region, the so called exclusion zone, around the MeNB within which the transmissions from the HeNB are interfered if a terminal happens to be connected to/camped on the HeNB. This can lead to problems both in connected mode and in idle mode such as 1) the terminal being unable to reliably decode paging channel resulting in missed pages and therefore the inability to receive terminal-terminated calls; 2) the terminal being unable to read common control channels; and 3) throughput degradation or degraded physical downlink shared channel (PDSCH) performance.
Thus, there is a need for method and apparatus that mitigates downlink control channel interference.